This invention is directed towards a two point system for mounting a spiral spring. While the term spiral spring will be used to describe the present invention, it is understood that the term spiral spring includes springs of similar designs which are sometimes termed clock wound springs or power springs. Normally, spiral springs are manufactured from a series of windings of a flat piece of spring wire material. Most of these springs have multiple coils generally having unrolled lengths of between 10 and 50 inches depending on the requirements of the particular application. Typical applications for these springs are counter-balances for vehicle windows, vehicle hoods or vehicle trunk lids.
When spiral springs are loaded, the coils are forced to one side causing adjacent coils to come into contact and position the spiral spring in a non-concentric position as illustrated in FIG. 1. In the non-concentric position, the contact of the coils creates a source of adjacent coil friction. This load in the coils caused by this adjacent coil friction will continue to build up as the spiral spring is wound until the load on the coils exceeds the frictional force holding the coils in contact with each other. The adjacent coils will then jump to a new position in contact with each other and the process will begin again. The continued build up of load and sudden release of the adjacent coils will have a chattering affect of the coils. The chattering of the coils can create an objectionable noise that will occur every time a trunk lid, a window or a hood is cycled.
Most of today's applications of spiral springs require some form of rust preventative coating. Because of the adjacent coil contact of the spiral spring in a loaded condition, applying the rust preventative after the assembly of the spring is not a viable option. Therefore, the rust preventative must be applied to the spring in an unloaded condition thus eliminating the opportunity of applying the rust preventative along with the mating components in an assembled condition.
Various attempts have been made at reducing or eliminating this adjacent coil friction build up. One method of reducing the amount of friction is to lubricate the coils prior to loading when the coils are in a concentric arrangement. This has the effect of lowering the coefficient of friction between adjacent coils and thus the load at which the adjacent coils will slip. The problems associated with lubrication of the coils is that it is a costly operation, and the lubricant will eventually be removed or squeezed out from in between the coils without the opportunity of having it replaced. The spiral spring is then operating as a non-lubricated spring with the associated chattering and noise problems.
U.S. Pat. No. 4,921,230 issued May 1, 1990 to H. Jay Thomsen discloses a method of eliminating adjacent coil contact and maintaining concentric coils of a spiral spring in a loaded condition. Thomsen discloses a clip which is part of the mounting of the spiral spring. The outer coil of the spring rides against the clip, the clip then stopping the movement of the spiral spring to a non-concentric position. While the retention clip in Thomsen works satisfactorily, it requires an additional piece and the orientation of the clip with respect to the spring must be maintained during the operation of the mechanism.
U.S. Pat. No. 3,091,447 issued May 28, 1963 to A. W. Donkin discloses another method of eliminating adjacent coil contact. Donkin uses a spring which is wound in an initial non-concentric form. The non-concentrically wound spring is used in conjunction with a two contact point staking arrangement. When load is applied to the spring, the spring has the tendency to move from its original non-concentric shape into a shape where the coils are concentric. The two contact point staking arrangement is either a two pin mounting system or an elongated bar contacting the spring at two points on the same side of the spring. The requirement of using a spiral spring having non-concentric adjacent coils presents both manufacturing problems and higher costs.
Accordingly, what is needed is a mounting system for a standard spiral spring which is simple, low cost and is able to maintain the concentric shape of the spiral spring after the spring is loaded and during the operation of the mechanism to which the spring is attached.